Cytology - PDF

Cytology By Dr. Esam El-Shwihy  Light microscope – Ordinary stain – Basophilia: binding with the basic stain (hematoxylin) – Acidophilia: binding with the acidic stain (eosin) – Special stains Electron microscope – Electron dense: dark – Electron light (l...

Cytology By Dr. Esam El-Shwihy  Light microscope – Ordinary stain – Basophilia: binding with the basic stain (hematoxylin) – Acidophilia: binding with the acidic stain (eosin) – Special stains Electron microscope – Electron dense: dark – Electron light (lucent): pale  CYTOLOGY - Cytology means the study of cells. - The cell is the structural and functional unit of the organism. It consists of: 1- Cell membrane (plasmalemma). 2- Protoplasm, the living substance of the cell, is subdivided into two compartments, the cytoplasm and the nucleus. The Cytoplasm contains: 1- Cytosol: It is the semifluid cytoplasmic matrix. 2- Organelles: They are the living active structures that are essential for the life of the cell. 4- Inclusions: They consist of storage forms of various nutrients and pigments. They are not essential for the life of the cell. Nucleus is formed of: 1- Nuclear envelope. 2- Nucleolus. 3- Chromatin 4- Nuclear matrix.  CELL MEMBRANE - All cells are bounded by a cell membrane (plasma-membrane or plasmalemma). Functions : 1- It maintains the structural integrity of the cell. 2- It controls movements of substances in and out the cell (selective permeability). 3- It can recognize antigens, foreign cells as well as altered cells. Structure: Light microscope (L/M): Cell membranes are not visible with the light microscope. Electron microscope (E/M): it is 10 nm thick and appears as two electron-dense lines separated by one electron-lucent intermediate zone (trilaminar appearance). Intracellular membranes are also trilaminar and called unit membrane. Molecular structure (The fluid-mosaic model) : -the cell membrane consists mainly of: 1. Phospholipids bilayer 2. Cholesterol 3. Proteins I) Phospholipids bilayer: - It is formed of double layer. - Each layer is formed of: Polar hydrophilic phosphate heads Non-polar hydrophobic tails of long fatty acid chains II) Cholesterol molecules: - They fill the gaps between the fatty acid tails and prevent their close packing. III) Membrane Proteins: Two types: A) Integral (intrinsic) proteins: They are present within lipid dilayer. They constitutes the fluid-mosaic model for membrane structure. B) Peripheral Proteins: They are associated with the surfaces of the bilayer.  Cell coat (Glycocalyx) - It is associated with the external surface of cell membrane. - It consists of short chains of glycoprotein and glycolipids. - Functions: recognition, protection and intercellular adhesions.  Passage of materials across cell membrane Passive transport: The passage of molecules depends on their concentration gradients. No energy is needed during this process. Active transport: Certain ions and molecules are transported against their concentration gradient from low concentration to higher one (e.g. sodium-potassium pump). Energy is required in this process. The process is carried out by carrier proteins. Vesicle-mediated transport: - The process includes either getting substances into the cell (endocytosis) or getting them out of the cell (exocytosis). 1- Endocytosis: Three forms: A) Pinocytosis (cell drinking): The cell entraps extracellular fluid or forming the pinocytotic vesicle. C( Phagocytosis (cell eating): It means cell eating. It is the process of engulfing large particles e.g. bacteria, microorganisms by specialized cells known as phagocytes as macrophages. B) Receptor mediated endocytosis: Specific receptors for substances (ligands) are located at the cell surface. Binding of a ligand to its receptor forms ligand-receptor complex in shallow invagination of cell membrane called coated pit. Coated pits become deep and pinch off the cell membrane are known as coated vesicles, which carry ligand-receptor complex into the cell. By endosomes, receptors are dissociated from ligands by the acidic pH. Recycling of receptors to cell membrane and digestion of ligand by lysosomes occur. 2- Exocytosis: It refers to release of cell products into the extracellular compartment.  MITOCHONDRIA Mitochondria are membranous organelles. Structure: - L/M: Mitochoindria need special stains stained blue by iron haematoxylin and green with Janus green. - E/M: Each mitochondrion possesses a smooth outer membrane and folded inner membranes. The folds of the inner membrane are called cristae. The large space enclosed by the inner membrane is known as the matrix space. Protein particles (elementary particles) are attached to cristal membrane by a short stem. The heads of elementary particles has ATP synthetase activity. They form ATP. The matrix space is filled with dense fluid composed of: 1- Enzymes of kreb’s cycle (citric acid cycle). 2- Ribosomes. 3- RNA: Transfer and messenger RNA. DNA. 4. Dense granules consisting of Ca+ ions. Function of Mitochondria: Mitochondria are the power houses of the cell They concentrate calcium to protect the cell from calcium toxicity. Mitochondria possess their own DNA & RNA, so they can synthesize their proteins (e.g. enzymes). Mitochondria are self replicating organelles through simple fission.  RIBOSOMES Ribosomes aro non-membranous cell organelles. They are formed in nucleolus - Ribosomes may be: 1- Free ribosomes: are present scattered in the cytoplasm. 2- Attached ribosomes forming the rough endoplasmic reticulum (rER). Structure - Ribosomes consist of two thirds rRNA and one third protein. - L/M: Free ribosomes cause diffuse basophilia. Attached ribosomes cause localized basophilia. - E/M: Each ribosome consists of two subunits, one is large and the other is small. The smaller subunit has a binding site for mRNA molecule while the large subunit has two binding sites for the tRNA. Ribosomes are held together by mRNA forming polysomes, which may be free or attached to rER. Function: Free ribosomes are responsible for synthesis of structural proteins for internal use of the cell. Attached ribosomes are responsible for synthesis protein which will be extruded outside cells as secretory proteins and lysosomal enzymes proteins.  ENDOPLASMIC RETICULUM (ER) They are membranous organelles There are two types of ER: Smooth endoplasmic reticulum (sER) without attached ribosomes. Rough endoplasmic reticulum (rER) with attached ribosomes. Both are continuous with each other. A- Smooth Endoplasmic Reticulum (sER) LM:  - It gives acidophilia in the cytoplassm. EM: - It is made of smooth-surfaced network of anastomosing tubules without ribosomes. Function of sER: Detoxification of drugs. Glycogen breakdown to glucose (glycogenolysis) and conversion of glucose into glycogen (glycogenesis).  Lipid synthesis Regulates the calcium level essential for muscular contraction. B- Rough Endoplasmic Reticulum (rER) - It is a membranous organelle. L/M: It gives localized cytoplasmic basophilia. E/M: It consists of an interconnecting network of membranous tubules, vesicles and flattened sacs (cisternae). Its outer surface is studded with ribosomes. Functions of rER: rER synthesizes proteins that are: Secretory proteins. Lysosomal enzymes. sER may be derived from rER.  GOLGI APPARATUS It is a membranous cell organelle. Structure: L/M: Golgi can be seen after special techniques e.g. silver In secretory cells it is supranuclear. In nerve cells it is around the nucleus. Negative Golgi Image: After H&E staining in cells with intensely basophilic cytoplasm such as plasma cells, Golgi apparatus appears as, clear unstained area near the nucleus called negative image of Golgi. E/M : Golgi apparatus is composed of:  1- Golgi stacks: Each stack consists of flattened cisternae (saccules). Each stack has: a) Cis-face (immature face) which is directed towards rough endoplasmic reticulum. b) Trans-face (mature or secretory face) is directed towards the plasmalemma. II- Transport [transfer] vesicles: They pinch off from rER and migrate to cis-face of Golgi. They carry newly synthesized polypeptides formed in rER.  III- secretory vesicles: They bud off from the trans-face of Golgi stacks. They contain secretory products and release their contents by exocytosis. Primary lysosomes arise also from trans-surface of Golgi. Functions of Golgi apparatus: Modification and concentration of the newly synthesized proteins.  LYSOSOMES Lysosomes are membranous cell organelles. They constitute an intracellular digestive system. They contain a variety of hydrolytic digestive enzymes. Lysosomal enzymes are synthesized in rER and transported in vesicles to Golgi complex. Types of lysosomes: A- Primary Lysosomes: They are newly formed lysosomes from trans-face (mature face) of Golgi. They are homogenous. B- Secondary Lysosomes: The contents of secondary lysosomes are heterogeneous.  They are formed after fusion of primary lysosomes with some other substances. When primary lysosome interacts with pinocytotic vacuole it gives multivesicular body. When primary lysosome interacts with phagocytic vacuole it gives phagosome. When primary lysosome interacts with autophagic vacuole it gives autophagosome. Functions: 1- Cellular defense by destruction bacteria. 2- Replace-ment of dead organelles. 3- Autolysis of tissue after death.  CENTRIOLES  They are non membranous organelles. L/M: Centrioles are paired cylinders arranged perpendicular to each other located near the nucleus and are called the centrosome. EM Its wall is made up of nine bundles of microtubules, each bundle consists of three microtubules (triplets). Function: 1) 1- They form the mitotic spindle during cell division. 2) 2- They form basal bodies of the cilia and flagella.  CILIA AND FLAGELLA CILIA  Non-membranous organelles.  Sites: Cilia are present in some cells of respiratory system, female and male genital tracts. Flagellum is only present in the sperm in human. Each cilium or flagellum is composed of basal body and shaft (axoneme). 1) The basal body is a typical centriole (nine triplets of microtubules). 2) The axoneme: The axoneme is formed of outer nine doublets of microtubules surrounding central two singlets microtubules. Radial spokes projecting from subunit A of the doublet toward the central sheath. Two dynein arms has ATPase activity radiates from A subunit to B subunit of adjacent doublet. Each A subunit has.  CELL INCLUSIONS  Inclusions are non-living components of the cell they include: I- Stored foods: 1- Fat droplets are stored mainly in fat cells. 2- Carbohydrates are stored in the form of glycogen which is abundant in liver cells and muscle fibers. II- Pigments: - Pigments are materials with natural colors and are classified into two types. 1- Exogenous pigments: They enter the body from outside e.g. Carotenes (yellowish or red pigment) are present in some vegetables as carrots and they are soluble in fat giving it its color. Minerals e.g. lead (blue) & silver (grey). Carbon: black particles that are prominent in the lung being phagocytosed by pulmonary macrophages. Tattoo, a process by which pigments are introduced into deep layers of skin. 2- Endogenous pigments: They are formed inside the body e.g. Hemoglobin (cause red color of the blood) Melanin, the dark brown or black pigment found in the skin, hair and eye. Lipofuscin pigment: It is yellowish brown granules that increase with age.  THE NUCLEUS - The nucleus is present in all eukaryotic cells except mature erythrocytes and blood platelets. - It contains the genome (genetic information). Number: The majority of cells have only one nucleus, some cells e.g. liver cells and cardiac muscle fibers are binucleated, and few others e.g. skeletal muscle fibers and osteoclasts are multinucleated. Staining: The nucleus is basophilic because of its content of nucleic acids (DNA & RNA).  INTERPHASE NUCLEUS (non-dividing nucleus) This is the nucleus of an interphase cell (non-dividing cell between cell divisions). consists of the following components: 1) Nuclear envelope. 2) Chromatin. 3) Nucleolus or nucleoli. 4) Nucleoplasm or karyoplasm.  NUCLEAR ENVELOPE It consists of two parallel membranes, each is a unite type membrane of about 7.5nm thickness separated by a 10-30nm space known as perinuclear space. - The inner nuclear membrane is associated with the peripheral chromatin. - The outer nuclear membrane has ribosomes and is often continuous with rough endoplasmic reticulum (rER).  - The nuclear envelope is not continuous, but form nuclear pores. CHROMATIN It is the hereditary material of the cell In the interphase nucleus, chromatin has two forms: A) Euchromatin (extended) which is the active form. B) Heterochromatin (condensed) which is the inactive form.  Structure of chromatin: Chromatin is composed mainly of DNA combined with basic proteins known as histones. There are five types of histones which are H1, H2A, H2B, H3 and H4.  NUCLEOLUS It is a dense non- membranous structure located in the nucleus. It is observed only during interphase and disappear during cell division. L/M, it is deeply basophilic due to its content of (RNA). E/M: the nucleolus consist of three distinct components, which are: Pars amorpha: pale centers with fine threads of chromatin representing chromosomes 13, 14, 15, 21 and 22 in humans (nucleolar organizers) encoding rRNA. Pars fibrosa: Containing newly formed rRNA surrounding the fibrillar center. Pars granulose (nucleolenema) having granular appearance and it is the site in which ribosomal subunits are assembled.